This invention relates to apparatus for handling plastic film articles, and is more particularly directed to apparatus known as a vacuum wicketter, which picks up film articles such as plastic bags on a manufacturing line, and rotates to carry the same to a station where the plastic bags are placed on a wicket. Vacuum is applied to arms of the rotating wicketter at least from the pickup work station to the wicketting work station.
A conventional vacuum wicketter is of aluminum construction, having a two-part hub assembly and a plurality of vacuum arms. The hub assembly has a lower stationary part and an upper rotating part. Both of these are typically formed of cast aluminum. A bearing mounted on the lower stationary part permits rotation of the superposed upper rotating part. One or more vacuum lines are connected to the stationary hub part, and these connect to semi-circular channel that is open on the upper surface of the stationary part.
The rotating hub part carries the vacuum arms which radiate from its circumference at an even spacing. Typically, there are six arms spread at 60 degrees or eight arms spaced at 45 degrees. L-shaped passages in the rotating hub part have one end open to the circumference, which serves as a socket for the male end of the arm, and the other end open to the lower surface to communicate with the vacuum channel in the stationary part. This ensures that vacuum is applied while the respective arms rotate over an angular sector corresponding to the travel between the pickup station and the wicketting work station.
The arms are typically aluminum and generally have a square or rectangular cross section. On each arm, the surface that faces in the direction of rotation has an elongated vacuum channel and a number of apertures or perforations to permit the arm to pick up and carry the plastic bag or other film articles. There is also conventionally a ceramic coating on this surface to withstand wear from friction of the plastic film against the arm.
However, with this construction there are a number of ensuing problems which can lead to breakdowns or to long outages for maintenance. These problems arise largely because of plastic debris and dust which is sucked by the vacuum into the tubular arm, and which can accumulate and clog the apparatus.
The male portions of the all-aluminum wicketter arms have a circular cross section to fit into the sockets which are machined or drilled into the aluminum rotating hub portion. However, the remainder of the arm is of square or rectangular cross section. There are blind pockets where the circular and square cross-sectional portions meet, and these provide sites for collecting the plastic dust and debris. This particulate matter quickly builds up and eventually will clog the arm, so that it will not operate as intended.
These tubular aluminum arms invariably have a plate that is either welded on or formed unitarily at the outer end of the arm, and which closes it off. Therefore, in order to clean dust and debris from the arm, it is necessary to remove the entire arm from the rotor hub. This takes considerable time and skill.
Furthermore, the ceramic surface on the aluminum arms eventually will wear off. At that point, the entire arm has to be removed and replaced, with the original arm being sent out for resurfacing. This is a rather expensive process, and there is significant down time for the arms to be removed and replaced.
Still another drawback with the conventional wicketter is that the two-part hub requires an additional bearing member between the stationary and rotating hub portions. This bearing can wear out, and it is difficult and time consuming job to replace it.
An improved rotary vacuum wicketter is disclosed in my earlier U.S. Pat. No. 4,877,233, granted Oct. 31, 1989. In that device, both the rotary and stationary hubs are molded of a plastic synthetic resin which has been filled with a suitable lubricating agent. The sockets for the radial arms can be formed of square cross section, so that the arms themselves can be tubes of uniform, square cross section. This avoids the blind corners of the prior art, and thus avoids the problem of clogging described earlier. The arms themselves can have a detachable and replaceable plastic wear plate screwed or otherwise fastened on, thus avoiding the expense and delays associated with resurfacing. In addition, the tubular arms have detachable end caps which permit cleaning and servicing of the arms without removal from the rotary hub.
However, the rotary and stationary hub portions are each one-piece members. When the facing surfaces become worn to the point where surface refinishing or replacement of the hub portions becomes necessary, then it is necessary to remove one or both of the rotary and stationary hub portions from the axial spindle, which involves significant machine down-time. Also, if wear is significant, the entire hub portion may need to be replaced.
In addition, the system of U.S. Pat. No. 4,877,233 requires special clamps to hold the arms in place on the hub and the square-cross section L-shaped channels in the rotary hub portion are somewhat difficult to mold, although these are certainly less difficult to create them similar shaped machined channels in the all-aluminum hubs.